Still he kept going. Until today. “His Royal Highness The Duke of Edinburgh has decided that he will no longer carry out public engagements from the autumn of this year,” Buckingham Palace announced.

Why did Prince Philip announce his retirement now?

The reason for the timing likely has to do with the pattern of his work schedule in 2017:

January: 0 engagements

February: 7 engagements

March: 21 engagements

April: 12 engagements

The contrast between March and April is particularly striking. Prince Philip was ramping up his workload in March, undertaking more and more engagements. Then, in April, a sharp drop off in the middle of the month, with only three engagements after Easter Sunday.

Prince Philip’s retirement may have jolted royal watchers, but it was long telegraphed.